Conventionally, a specimen substrate including a wafer or a mask is observed, for example, in the semiconductor manufacturing field. Optical microscopes and scanning electron microscopes (SEMs) are known as conventional observation devices. The use of a projection-type observation device has also been suggested. A projection-type observation device irradiates with an electron beam of a diameter larger than that of an SEM and acquires a specimen image over a wide area.
By the way, recently, patterns of specimens have become finer and the sizes of foreign materials to be detected have also become smaller. For example, the pattern sizes have become 100 nm or less. It is desired to detect foreign materials of 100 nm or less. Conventional optical microscopes, however, have insufficient resolution and have difficulty in observing such fine objects. SEMs can increase the magnification and can observe even fine objects, but would require an immense amount of observation time. The use of an observation device of a projection type would require short observation time but provide insufficient resolution.
As mentioned above, conventional observation techniques would have a limitation in object size and have difficulty in observing fine-sized objects. It would also not be easy to provide sufficient capability required to observe various objects. The background art will next be described in more detail from four points of view.
[Background 1] (Observation of Foreign Materials)
Electron Beam Inspection Method and Electron Beam Inspection Device
In this background art, the present invention relates to an electron beam inspection method and an electron beam inspection device, and in particular to an electron beam inspection method and electron beam inspection device for irradiating a specimen with an electron beam, detecting reflected electrons by means of a detector, and thereby acquiring an image of a foreign material on the specimen surface.
Japanese Patent Laid-Open Application No. Hei 11-108864 discloses a conventional pattern defect inspection device. This conventional device has a means of irradiating a specimen surface with an electron beam emitted from an electron source. An area of a certain square measure is simultaneously irradiated with the electron beam. The conventional device also has: a movable specimen stage for holding a specimen; a means of applying a voltage which causes the electron beam with which the specimen is irradiated to be reflected immediately in front of the specimen surface; a means of forming an image having a certain area from the electron beam reflected immediately in front of the surface; and a means of converting the image to an electrical image signal. With the above-mentioned configuration, the conventional device acquires an image signal of an area of a certain square measure on a specimen surface, compares the acquired image signal to an image signal of another area, and detects a pattern defect.
The above-mentioned conventional device can detect a pattern defect on a specimen surface. The conventional device, however, cannot effectively detect a foreign material present on a specimen surface.
On the other hand, dust or other foreign materials may sometimes stick to the surface of a specimen, such as a semiconductor wafer, during processes. Detection of foreign materials is important for the quality control of semiconductor wafers. However, taking a long time for foreign material inspection is not preferable from a productivity point of view.
It is thus desired to provide an electron beam inspection method and electron beam inspection device capable of quickly and reliably detecting a foreign material on a specimen surface.
[Background 2] (Observation of Insulating and Conductive Areas)
Specimen Observation Device, Specimen Observation Method, and Semiconductor Manufacturing Method Using the Device and Method
In this background art, the present invention relates to a specimen observation device, a specimen observation method, and a semiconductor manufacturing method using the device and method, and in particular to a technique for irradiating a specimen surface on which insulating and conductive areas are formed with a low-energy imaging electron beam to acquire an image of the specimen surface.
Published Japanese Translation of PCT International Publication for Patent Application No. 2003-500821 discloses a conventional secondary electron emission microscope. This conventional device first irradiates with a high-energy first beam. The first electron beam, having a collision energy of the order of 1 keV, is a beam suited for parallel multi-pixel imaging. The first beam neutralizes the charge of a sample, or causes a positive charge to accumulate. The conventional device then irradiates with a low-energy beam with a collision energy of 0 eV. The positive charge of the sample surface is compensated, and the surface potential of the sample is fixed to a predetermined voltage value. Secondary electrons are generated in this state. An image can thus be acquired from the secondary electrons without a problem of charge accumulation.
However, the above-mentioned conventional device detects only secondary electrons emitted from the sample, and acquires an image only from the secondary electrons. Secondary electron emission totally follows the cosine law and has a poor straight-advancing characteristic. As a result, it would be difficult to acquire an image with a good signal-to-noise ratio.
In a case where insulating and conductive areas are formed on a sample surface, an image acquired only from secondary electrons does not indicate a very high material contrast between the insulating and conductive areas. Consequently, observation or inspection of the sample surface may be difficult.
For example, suppose that insulating and conductive areas on a sample are unbalanced and the square measure of the insulating area is overwhelmingly larger than that of the conductive area (the area ratio of the insulating area is very large). In this case, an image from secondary electrons would provide a low contrast between the insulating and conductive areas, and therefore the inspection might be difficult.
For this reason, it is desired to provide a technique capable of observing a specimen surface with a high contrast in a case where insulating and conductive areas are formed on the specimen surface.
[Background 3] (Observation of Patterns)
Specimen Observation Method and Device, and Specimen Inspection Method and Device Using the Method and Device
In this background art, the present invention relates to a specimen observation method and device for observing a pattern of a specimen using an electron beam, and in particular to a fine pattern observation technique using an electron beam with a low landing energy.
Conventionally, a specimen substrate including a wafer or a mask is observed, for example, in the semiconductor manufacturing field. Specimen observation is performed for structural evaluation, observation under magnification, material evaluation, inspection and observation of an electrical conduction state, or the like. High precision, high reliability, high throughput, and the like are required in inspection of specimen substrates. So, it is desired to provide a specimen observation technique that meets these requirements. Specimen observation and inspection techniques are also important in device manufacturing processes. Specimens are semiconductor materials, LSIs, metallic materials, insulating materials, and the like.
Optical microscopes or electron beam observation devices are conventionally used for observing patterns on specimens. Scanning electron microscopes (SEMs) are known as typical electron beam observation devices. An SEM scans a specimen with an electron beam and thereby allows the observation to be done with a high magnification. An observation technique using an SEM is disclosed, for example, in Japanese Patent Laid-Open Application No. 2004-177446.
Observation devices using projection optical systems have also been suggested as electron beam observation devices. Observation devices of this type are hereinafter referred to as projection-type observation devices. A projection-type observation device irradiates a specimen with an electron beam of a diameter larger than that of an SEM, and generates an image of an area corresponding to the diameter of the electron beam. Such an observation device is disclosed, for example, in Japanese Patent Laid-Open Application No. Hei 11-108864.
By the way, recently, patterns on specimens have become finer, and pattern sizes (width or the like) have reached 100 nm or less. As a result, it has become difficult to observe a pattern and pattern defect of a specimen with conventional observation techniques.
That is, optical observation is limited in resolution by the wavelength of light. If the pattern size is 100 nm or less, the pattern size is smaller than the wavelength of light, so that sufficient resolution cannot be obtained and it becomes difficult to detect a pattern defect.
The resolution of pattern observation and pattern defect inspection using an SEM can be increased by reducing the spot size of the electron beam. Accordingly, even if the pattern size is 100 nm or less, pattern observation can be done and pattern defect inspection can also be done. However, the pixel size requires reducing in order to observe fine patterns, so an immense amount of time is required for the observation. For example, the pixel size of the order of 10 nm is applied in order to detect a defect of 50 nm. In this case, even an inspection performed at 200 Mpps (Mega pixel per second) would take 1.4 hours per square centimeter. The inspection thus requires an immense amount of time and is impractical.
A projection-type observation device is configured to irradiate a specimen with an electron beam of a large diameter and generate an image of a wide area, thereby allowing the observation to be performed in a shorter amount of time than SEMs. However, the device cannot provide a sufficient contrast and sufficient resolution when the pattern size is 100 nm or less.
More specifically, in a projection-type observation device, a primary optical system irradiates a specimen with an electron beam, and a secondary optical system generates an image of secondary electrons emitted from the specimen. The imaging area (beam irradiation area) can be set to tens of micrometers or more, and the observation time is short. However, aberrations of the secondary optical system cannot be sufficiently reduced, and it is not easy to realize a resolution required for observation for the pattern size of 100 nm or less.
In the above-mentioned background, it is therefore desired to provide a technique capable of observing fine patterns.
[Background 4] (Observation of a Specimen in which a Plurality of Films are Formed)
Inspection Method and Inspection Device for a Film-Coated Substrate
In this background art, the present invention relates to an inspection method and inspection device for a film-coated substrate, and in particular to an inspection method and inspection device for a film-coated substrate for inspecting a film-coated substrate using a charged particle beam.
Japanese Patent Laid-Open Application No. 2004-177446 discloses a conventional mask inspection device. This conventional device inspects a mask including a reticle on which a device pattern to be transferred onto a sensitive substrate is formed. The conventional device comprises an imaging means, a storage means, and a comparison means. The imaging means irradiates an object to be inspected with an electron beam, and converts an electron beam transmission image or a secondary electron image (SEM image) of the device pattern to obtain actual image data of the pattern. The actual image data is the object to be inspected. The storage means stores design data of the pattern and reference image data that meets the design criteria. The comparison means compares the actual image data and the reference image data.
The above-mentioned conventional device inspects a mask by comparing image patterns. For this reason, the conventional device can only inspect for the presence or absence of a defect in a device pattern on the mask surface. Consequently, the conventional device would not be able to inspect the shape under the surface, the presence of a foreign material, and the like.
It is therefore desired to provide a technique capable of detecting the shape of a substrate and the shape of a lower layer film or the like which are present under the surface of a film-coated substrate. It is also desired to provide a technique capable of detecting a foreign material or the like present in a lower layer film or the like.